Projector and optical device

ABSTRACT

To provide a projector or the like, which use a solid-state light-emitting element as light source and which provides a bright, stable, and uniform projection image, the present invention includes: a light source to emit light; a spatial light modulator to modulate the light from the light source in accordance with an image signal; and a projector lens to project the light modulated by the spatial light modulator. The spatial light modulator is a tilt mirror device including a movable mirror element that reflects the light from the light source in the direction of the projector lens or in the direction other than that of the projector lens. The invention may further include a light-intensity measuring section provided in an imaging position of the light source or in the vicinity of the imaging position to measure the light intensity of the light reflected in the direction other than that of the projector lens; and a light-source controller to control the light source in accordance with the signal from the light-intensity measuring section.

BACKGROUND OF THE INVENTION

This is a Continuation of application Ser. No. 11/151,208 filed Jun. 14,2005, which is a Continuation of application Ser. No. 10/826,409 filedApr. 19, 2004, now U.S. Pat. No. 6,953,251. The disclosures of the priorapplications are hereby incorporated by reference herein in theirentireties.

1. Field of Invention

The present invention relates to a projector and, more particularly, toa projector and an optical device using a solid-state light-emittingelement as light source.

2. Description of Related Art

Since solid-state light-emitting elements, such as light-emitting diodeelements and semiconductor laser devices, have extremely high efficiencyof converting electricity to light and are compact and lightweight, theyhave wide applicability in lighting. Related art or known methods ofcontrolling the light intensity of the solid-state light-emittingelements include an electrical feedback method by constant-currentdriving or the like (for example, see JP-A-1-116692, JP-A-63-307784 andJP-A-63-226079) and a feedback control method by measuring lightintensity (for example, see JP-A-1-239969, JP-U-62-071642 andJP-A-63-027073).

SUMMARY OF THE INVENTION

Projectors are devices that display images by projecting light(projection light) in accordance with image signals transmitted fromimage transmitters, such as computers. Solid-state light-emittingelements can be used as the light sources of the projectors. Theprojectors are required to be space-saving and portable, thus tending tobe more compact and lightweight. Ultrahigh pressure mercury lamps whichhave been used as a light source can emit high-intensity light butrequire large and heavy drive circuits, thus preventing the downsizingand weight reduction of the projectors. Solid-state light-emittingelements are compact and lightweight and so the use of the solid-statelight-emitting elements simplifies illumination optical systems.Accordingly, the use of the solid-state light-emitting elements as alight source promotes downsizing and weight reduction of the projectors.Some related art solid-state light-emitting elements have increasedluminescence, long lifetime and low power consumption, thus beingsuitable for the light source of the projectors.

Spatial light modulators of projectors may use tilt mirror devices. Oneof the tilt mirror devices is a digital micromirror device (hereinafter“DMD”) of Texas Instruments Inc. The DMD includes a movable mirrorelement that reflects light from a light source toward a projector lensor in the direction other than that of the projector lens. A Projector,which uses solid-state light-emitting elements as a light source andcombines the solid-state light-emitting elements with a DMD, are notknown.

It is desirable that the light of the light sources of the projectors beuniformly bright and stable in light intensity to project bright andstable projection images. When a plurality of solid-state light-emittingelements are used in the projectors to obtain sufficient lightintensity, the variations in light intensity of the solid-statelight-emitting elements cause non-uniform light intensity of theprojection images. Therefore, the individual solid-state light-emittingelement desirably has stable and uniform output.

When stabilizing and uniformizing the light intensity of the solid-statelight-emitting elements used as the light sources of the projectors byusing related art, the use of the solid-state light-emitting elements asthe light sources of the projectors requires large outputs. The largeoutputs cause significant physical change of the solid-statelight-emitting elements due to heat generation over their lifetime. Theabove-mentioned drive-current control method of stabilizing the outputby the constant-current driving or sensing the electrical conditioncannot cope with the physical changes of the solid-state light-emittingelements, having difficulty in sufficiently stabilizing the lightquantity.

The control method of monitoring the light intensity of the solid-statelight-emitting elements to control the drive current can cope with thechange of the physical characteristics of the solid-state light-emittingelements over time. However, in the projector, when light-receivingelements to monitor light intensity are arranged near the light sources,the light is blocked off by the light-receiving elements todisadvantageously make the projection images dark. Also, when thelight-receiving element to monitor light intensity is arranged in thevicinity of each of the solid-state light-emitting elements to stabilizethe light intensity of each solid-state light-emitting element and touniformize the luminance of the solid-state light-emitting elements, thestructure becomes more complicated, making it difficult to dispose.

The present invention addresses the above and/or other problems.Accordingly, the invention provides a projector which uses a solid-statelight-emitting element as light source and which provides a bright,stable, and uniform projection image.

In order to address or achieve the above, an aspect of the presentinvention provides a projector including: a light source to emit light;a spatial light modulator to modulate the light from the light source inaccordance with an image signal; and a projector lens to project thelight modulated by the spatial light modulator. The spatial lightmodulator is a tilt mirror device including a movable mirror elementreflecting the light from the light source in the direction of theprojector lens or in the direction other than that of the projectorlens. The projector further includes: a light-intensity measuringsection provided in an imaging position of the light source or in thevicinity of the imaging position to measure the light intensity of thelight reflected in the direction other than that of the projector lens;and a light-source controller to control the light source in accordancewith a signal from the light-intensity measuring section.

The projector that uses the tilt mirror device as a spatial lightmodulator includes a plurality of movable mirror elements to modulatelight by reflecting incident light in the direction of a projector lensand in the direction other than that of the projector lens. The lightreflected toward the projection lens forms a projection image, while thelight reflected in the direction other than that of the projector lensis wasted. The light reflected in the direction other than that of theprojector lens is measured by the light-intensity measuring section. Thelight source is controlled on the basis of the measured light intensity.The light from the light source is not directly measured in the vicinityof the light source. But the light reflected in the direction other thanthat of the projector lens by the spatial light modulator is measured.Accordingly, there is no need to dispose light-receiving elementsfunctioning as a light-intensity measuring section in the vicinity ofthe light source. Since the light-receiving elements are not arranged inthe vicinity of the light source, the optical path required to form aprojection image is not blocked off by the light-receiving elements.Since the wasted light that is not used for image formation is used forlight intensity measurement, the light to form a projection image is notlost even during image projection. Accordingly, a projector is providedin which the light source can provide stable light intensity withoutdecreasing the brightness of a projection image and which provides abright and stable projection image.

According to an exemplary embodiment, the light source may include aplurality of solid-state light-emitting elements; the light-intensitymeasuring section may include a plurality of light-intensity measuringelements corresponding to the plurality of solid-state light-emittingelements; and the light-source controller may control each of theplurality of solid-state light-emitting elements. Since thelight-receiving elements functioning as a light-intensity measuringsection are arranged in the image forming position of the solid-statelight-emitting elements or in the vicinity thereof, the light intensityfor each of the plurality of solid-state light-emitting elements of thelight source can be measured. The light intensity measurement of eachsolid-state light-emitting element allows the light intensity of thesolid-state light-emitting elements to be stabilized and uniformized.Accordingly, a projector that forms a bright, stable, and uniformprojection image is provided.

According to an exemplary embodiment of the invention an operation unitto perform a specified calculation based on the signal from thelight-intensity measuring section and outputting the calculation to thelight-source controller may be included. Accordingly, a projector, whichis capable of controlling light intensity in response to its useconditions or user's requirements, is provided.

According to an exemplary embodiment, the operation unit may perform thespecified calculation using the number of the movable mirror elementsreflecting the light from the light source in a direction other thanthat of the projector lens. Referring to the direction, in which themovable mirror elements point when the light from the light source isreflected in the direction other than that of the projector lens, as “anOFF-direction,” the light intensity measured by the light-intensitymeasuring section varies depending on the number of the movable mirrorelements in the OFF-direction in addition to the light intensity of allthe light from the light source. The calculation using the number of themovable mirror elements in the OFF-direction allows the output of thelight source to be calculated. Since the output of the light source canbe accurately controlled irrespective of the number of the movablemirror elements in the OFF-direction as above-described, the lightintensity of the light source can be always stabilized and uniformizedeven during image projection while the movable mirror elements are beingdriven. Accordingly, a projector that constantly forms a bright, stable,and uniform projection image can be provided.

According to an exemplary embodiment, the light source may include afirst light source to emit light in a first wavelength range and asecond light source to emit light in a second wavelength range differentfrom the first wavelength range; the first light source and the secondlight source arranged in approximately symmetrical positions withrespect to the projector lens; and the light-intensity measuring sectionincluding a first light-intensity measuring section and a secondlight-intensity measuring section. The first light-intensity measuringsection is arranged in the vicinity of the second light source and outof the light from the first light source, measures the light intensityof the light reflected in the direction other than that of the projectorlens. The second light-intensity measuring section is arranged in thevicinity of the first light source and out of the light from the secondlight source, measures the light intensity of the light reflected in thedirection other than that of the projector lens.

Since the light-receiving elements that measure the light from the firstlight source are disposed in the position in which the image of thefirst light source is substantially imaged and the light-receivingelements that measure the light from the second light source aredisposed in the position in which the image of the second light sourceis substantially imaged, the light-receiving elements can be arranged incorrespondence with the arrangement of the light sources. Since thelight-receiving elements that measure the light from the first lightsource are disposed in the vicinity of the second light source, whilethe light-receiving elements that measure the light from the secondlight source are disposed in the vicinity of the first light source, theintensity of the light of the light source can be stabilized anduniformized with a simple structure. Accordingly, a projector isprovided which forms a bright, stable, and uniform projection image witha simple structure.

The first light-intensity measuring section and the second light sourcemay be formed on an identical substrate, the first light-intensitymeasuring section being arranged among the plurality of solid-statelight-emitting elements of the second light source; and the secondlight-intensity measuring section and the first light source are formedon an identical substrate, the second light-intensity measuring sectionbeing arranged among the plurality of solid-state light-emittingelements of the first light source. In the tilt mirror device that is aspatial light modulator, the movable mirror elements selectively shiftthe position of their reflecting surfaces (reflecting angles). Since themovable range of the movable mirror elements is limited, the lightdeflection angle of the spatial light modulator is also limited. Themixed arrangement of the light-receiving elements among the solid-statelight-emitting elements on the light-source substrate maximizes theutilization of the light deflection angle of the spatial lightmodulator. This ensures the clearance between the light source and thebarrel of the projector lens, reducing or preventing spatialinterference therebetween.

The first light-intensity measuring section and the second light sourcemay be formed on an identical substrate, the first light-intensitymeasuring section being arranged in a region different from the secondlight source; and the second light-intensity measuring section and thefirst light source are formed on an identical substrate, the secondlight-intensity measuring section being arranged in a region differentfrom the first light source. Since the light-receiving elements arearranged in the region different from the solid-state light-emittingelements on the identical substrate, the light-receiving elements arethermally and electrically isolated from the solid-state light-emittingelements. Thus, the light-receiving elements are less influenced by heatpropagation and electrical noise from the solid-state light-emittingelements, thus making a measurement with less error. Accordingly, aprojector having a stable brightness and more accurate uniformity can beprovided.

A projector according to an aspect of the invention includes a lightsource to emit light; a spatial light modulator to modulate the lightfrom the light source in accordance with an image signal; a projectorlens to project the light modulated by the spatial light modulator; anda light-source controller. The spatial light modulator is a tilt mirrordevice including a movable mirror element reflecting the light from thelight source in the direction of the projector lens or in the directionother than that of the projector lens. The light source includes a firstlight source to emit light in a first wavelength range and a secondlight source to emit light in a second wavelength range different fromthe first wavelength range. The first light source and the second lightsource are arranged in approximately symmetrical positions with respectto the projector lens. The first light source receives the light fromthe second light source to measure the light intensity of the secondlight source. The second light source receives the light from the firstlight source to measure the light intensity of the first light source.The light-source controller controls the light source on the basis ofthe measured light intensity.

Since the solid-state light-emitting elements of the light sourcefunction as a time-division light-intensity measuring section when theyare emitting no light, there is no need to provide a separatelight-receiving element. Since the light-receiving element itself is notnecessary, the light intensity of the light source can be stabilized anduniformized with an inexpensive and simple structure without increasingthe number of parts. Accordingly, a projector is provided which forms abright, stable, and uniform projection image with a simple structure.

An aspect of the invention provides an optical device including a lightsource to emit light; a spatial light modulator to modulate the lightfrom the light source in accordance with an image signal; and an imaginglens to image the light modulated by the spatial light modulator onto aspecified surface. The spatial light modulator is a tilt mirror deviceincluding a movable mirror element reflecting the light from the lightsource in the direction of the imaging lens or in the direction otherthan that of the imaging lens. The optical device further includes: alight-intensity measuring section provided in an imaging position of thelight source or in the vicinity of the imaging position to measure thelight intensity of the light reflected in the direction other than thatof the projector lens; and a light-source controller to control thelight source in accordance with the signal from the light-intensitymeasuring section. Accordingly, an effective and stable optical deviceis provided in which the light intensity of the light source can bestabilized without decreasing efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a projector according to a first exemplaryembodiment of the present invention;

FIG. 2 is a schematic of the arrangement of solid-state light-emittingelements and light-receiving elements;

FIG. 3 is a schematic of an example of light intensity measurementtiming;

FIG. 4 is a schematic of an example of light intensity measurementtiming;

FIG. 5 is a schematic of a projector according to a second exemplaryembodiment of the invention;

FIG. 6 is a schematic of the arrangement of solid-state light-emittingelements and light-receiving elements;

FIG. 7 is a schematic of a projector according to a third exemplaryembodiment of the invention;

FIG. 8 is a schematic of the arrangement of solid-state light-emittingelements and light-receiving elements;

FIG. 9 is a schematic of a projector according to a fourth exemplaryembodiment of the invention;

FIG. 10 is a schematic of the arrangement of solid-state light-emittingelements;

FIG. 11 is a schematic of an example of the circuit of a switch sectionof an LED;

FIG. 12 is a schematic of an example of light-intensity measurementtiming;

FIG. 13 is a schematic of examples of an LED lighting timing and ahalf-toning timing; and

FIG. 14 is a schematic diagram of a printer according to a fifthexemplary embodiment of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present invention will be specifically described hereinafter withreference to the drawings.

First Exemplary Embodiment

FIG. 1 shows a schematic of a projector 100 according to a firstexemplary embodiment of the present invention. A light source 101 of theprojector 100 includes a plurality of light-emitting diodes(hereinafter, “LED”) which are solid-state light-emitting elements. TheLEDs of the light source 101 are driven by a light-source drive circuit103. The LEDs include an R-light LED 102R that emits red light(hereinafter, s “R-light”), a G-light LED 102G that emits green light(hereinafter, “G-light”), and a B-light LED 102B that emits blue light(hereinafter, “B-light”).

The light emitted from the light source 101 passes through a field lens105 and is then incident on a spatial light modulator 104. The fieldlens 105 has the function of illuminating the spatial light modulator104 in a telecentric manner. Specifically, the function of letting theillumination light into the spatial light modulator 104 as parallel aspossible to a principal ray. The projector 100 forms the image of thelight source 101 in the position of the entrance pupil of a projectorlens 106 to make Koehler illumination on the spatial light modulator104. The spatial light modulator 104 is a tilt mirror device, whichmodulates the incident light in accordance with an image signal. Oneexample of the tilt mirror device is a DMD of Texas Instrument Inc. Thelight modulated by the spatial light modulator 104 exits toward theprojector lens 106. The projector lens 106 projects the light emergingfrom the spatial light modulator 104 onto a screen 108.

The spatial light modulator 104 includes a plurality of movable mirrorelements (not shown). The movable mirror elements move selectivelybetween a first reflecting position and a second reflecting position inaccordance with the image signal to reflect the incident light towardthe projector lens 106 (ON) or in the direction other than that of theprojector lens 106 (OFF). The light advancing toward the projector lens106 forms a projection image on the screen 108.

The light source 101 lights on the R-light, G-light, and B-light LEDs insequence in one frame of the projection image to illuminate the spatiallight modulator 104. An observer integrates the R-light, G-light, andB-light, which are emitted from the light source 101 in sequence andmodulated by the spatial light modulator 104, to recognize them.Accordingly, a full-color projection image is formed on the screen 108.To obtain an entirely white projection image by the sequentialprojection of the R-light, G-light, and B-light, the amount of G-lightflux must be 60 to 80 percent of all the light flux. Assuming that theoutput amount and the number of the color-light LEDs are equal, theamount of G-light flux would become insufficient. Therefore, when theR-light, G-light, and B-light LEDs are arranged in equal numbers, thelighting time of the G-light LED is made longer than those of theR-light and B-light LEDs. When the G-light LEDs are arranged more thanthe R-light and B-light LEDs, the lighting time of the G-light LED canbe made equal to or shorter than those of the other color LEDs. Thisallows natural full color images to be provided.

The light, reflected from the spatial light modulator 104 to advance inthe direction other than that of the projector lens 106, is incident ona light-intensity measuring section 110. The light-intensity measuringsection 110 is arranged in the position on which the OFF-light from thespatial light modulator 104 is incident. More specifically, according tothe exemplary embodiment, the light-intensity measuring section 110 isarranged in the positions in which the LEDs 102R, 102G, and 102B formimages or in the vicinity thereof when all the movable mirror elementsare located in the positions corresponding to the OFF (light off) of thepixels. The position of the light-intensity measuring section 110 andthe positions of the LEDs 102R, 102G, and 102B are conjugate with eachother when all the movable mirror elements are located in the positionscorresponding to the OFF (light off) of the pixels. The light-intensitymeasuring section 110 includes light-receiving elements 110R, 110G, and110B, which are light-intensity measuring elements corresponding to theLEDs 102R, 102G, and 102B. The light-receiving elements may bephotodiodes, for example. The light-receiving elements 110R, 110G, and110B measure the light from the LEDs 102R, 102G, and 102B in thesubstantially imaging positions, respectively. The light-receivingelements 110R, 110G, and 110B then output the signals corresponding tothe respective light quantities of the LEDs to an operation unit 112.The operation unit 112 processes the signals outputted from thelight-receiving elements 110R, 110G, and 110B by a specified method andoutputs the calculations to a light-source controller 114. Thelight-source controller 114 controls the light-source drive circuit 103in accordance with the calculation outputted from the operation unit 112to control the output of the light source 101. For example, the initialvalues of the light intensity of the LEDs are stored in a memory (notshown) and a feedback control is performed using the initial value astarget values, so that the luminance of the light from the light source101 can be maintained stably in the initial values. Thus, the lightintensity of the LEDs 102R, 102G, and 102B can be maintained uniform.

The structure, in which the light intensity, or the outputs of the LEDs102R, 102G, and 102B is measured, allows the projector 100 to respond tothe physical change of the LEDs 102R, 102G, and 102B over time due toheat generation, lifetime and so on, and to control the light intensity.Since the light from the light source 101 is not directly measured butthe light from the spatial light modulator 104 is measured, there is noneed to arrange the light-intensity measuring section 110 in thevicinity of the light source 101. Since the light-intensity measuringsection 110 is not arranged in the vicinity of the light source 101, thepath of the light that forms a projection image is not blocked off bythe light-intensity measuring section 110. Since the waste light, whichis not used for image formation, is used to measure the light intensity,as described above, the light intensity of the light source 101 can becontrolled without losing the brightness to form a projection image evenduring image projection. This allows the light intensity of the lightsource 101 to be stabilized without losing the brightness of theprojection image, thus providing the projector 100 capable of projectingbright and stable images.

FIG. 2 shows a view seeing from the spatial light modulator 104 towardthe projector lens 106. Referring to FIG. 2, the arrangement of the LEDs102R, 102G, and 102B of the light source 101 and the light-receivingelements 110R, 110G, and 110B will be described. When all the movablemirror elements are located in the positions corresponding to the OFF(light-off) of pixels, the light-receiving elements 110R, 110G, and 110Bare arranged in the position in which the LEDs 102R, 102G, and 102B formimages or in the vicinity thereof. As described above, when all themovable mirror elements are located in the positions corresponding tothe OFF (light-off) of pixels, the R-light LED 102R and thelight-receiving element 110R, the G-light LED 102G and thelight-receiving element 110G, and the B-light LED 102B and thelight-receiving element 110B are conjugate with each other,respectively. The light-receiving elements 110R, 110G, and 110B detectthe light from the LEDs 102R, 102G, and 102B in conjugation therewith.Thus, the light from each of the LEDs 102R, 102G, and 102B can bedetected. The light-source controller 114 controls the light-sourcedrive circuit 103 in accordance with the signal outputted from thelight-intensity measuring section 110. The light-source drive circuit103 controls the respective drive currents of the LEDs 102R, 102G, and102B, thereby controlling the outputs of the LEDs 102R, 102G, and 102B.

The light intensity of each LED can be measured by arranging thelight-receiving elements 110R, 110G, and 110B in the image formingpositions of the LEDs 102R, 102G, and 102B or in the vicinity thereof.The measurement of the light intensity of each of the LEDs 102R, 102G,and 102B allows the light intensity of LEDs to be stabilized anduniformized. Batch control of the plurality of LEDs makes it difficultto uniformize the light intensity of the LEDs. Also, the batch controlof the plurality of LEDs also controls LEDs that require no lightintensity control, thereby applying an unnecessary load on the LEDs thatrequire no light intensity control. The application of the unnecessaryload would make the outputs of the LEDs unstable, thereby preventing thestabilization of the light intensity of each LED and promoting thedegradation of the LEDs. According to the exemplary embodiment, thelight intensity of each LED is controlled individually, allowing controlaccording to the condition of each LED, and thus providing the projector100 capable of projecting bright, stable, and uniform images withoutapplying an unnecessary load on the LEDs.

Referring now to FIGS. 3 and 4, the operation and the timing ofmeasuring the light intensity will be described. The timing charts ofFIGS. 3 and 4 are for one frame of an projection image, showing thedriving time (light-on time) of the LEDs 102R, 102G, and 102B, the imagesignals of the pixels, and the detection timings of the light-receivingelements 110R, 110G, and 110B, from the top. The charts of FIGS. 3 and 4are represented in a positive logic. The pixel is the minimum unit of aprojection image, which corresponds to the movable mirror element of thespatial light modulator 104. FIGS. 3 and 4 illustrate three pixels A, B,and C. An image transmitter (not shown), such as a computer outputsimage signals for all the pixels in the projection image to the spatiallight modulator 104. The spatial light modulator 104 drives the movablemirror elements in accordance with the image signals to modulate thelight. The image signals for the pixels at the timing other than thedetection timings of the light-receiving elements 110R, 110G, and 110Bcorrespond to the projected image and are arbitrary.

The movable mirror elements are driven in the direction of +θ or −θdepending on the image signals. Suppose that the light emitted from thelight source 101 into the spatial light modulator 104 is reflectedtoward the projector lens 106 when the movable mirror element is in thedirection of +θ, while when the movable mirror element is in thedirection of −θ, it is reflected in the direction other than that of theprojector lens 106. For the purpose of explanation, the orientation ofthe movable mirror element that reflects the light from the light source101 in the direction other than that of the projector lens 106, that is−θ direction, is hereinafter referred to as “OFF-direction.”

FIG. 3 shows the state in which timings TR, TB, and TG, at which all themovable mirror elements of the spatial light modulator 104 are pointedin the OFF-direction, are proactively provided to allow thelight-intensity measuring section 110 to measure the light intensity.When all the movable mirror elements of the spatial light modulator 104are in the OFF-direction, all the light from the light source 101 isapplied to the light-intensity measuring section 110, so that thelight-intensity measuring section 110 can measure the light intensity ofthe light source 101. The light-intensity measuring timing by thelight-intensity measuring section 110 is hereinafter referred to as “acalibration mode.”

Providing calibration modes TR, TB, and TG in each color-light frame(subframe), at least one time, allows the measurement of the lightintensity of the LEDs 102R, 102G, and 102B of the light source 101. Whenthe light source 101 includes a plurality of LEDs for each color light,the light intensity for the individual LED can be measured by providingthe calibration mode during the lighting of only the single LED for eachcolor. Thus, the light intensity can be controlled for each color lightor each LED.

The calibration mode can be set freely. The setting may be made at anytime during the image projection, for any frame, at the time theprojector 100 is turned on, at the time the drive current of the lightsource 101 fluctuates, at the time the ambient temperature of the lightsource 101 fluctuates and so on. In the example of FIG. 3, thecalibration mode is provided in each color-light frame in one frame ofthe projection image. However, it may be varied as appropriate. Forexample, one frame in the projection image may be set only in theR-light frame and the next frame may be set only in the G-light frame.

In the example of FIG. 3, the timing is proactively provided at whichall the movable mirror elements of the spatial light modulator 104 aredirected in the OFF-direction, being set as a calibration mode. In theexample of FIG. 4, the calibration mode is set irrespective of thenumber of the OFF-direction movable mirror elements, as shown by thetimings TR, TB, and TG. In this case, the operation unit 112 performs aspecified calculation using the number of the OFF-direction movablemirror elements in accordance with the image signal sent from the imagetransmitter (not shown).

The light intensity measured by the light-intensity measuring section110 varies depending on the number of the OFF-direction movable mirrorelements. The calculation using the number of the OFF-direction movablemirror elements allows the calculation of the light intensity when allthe movable mirror elements of the spatial light modulator 104 are setin the OFF-direction. For example, suppose that the spatial lightmodulator 104 includes three movable mirror elements corresponding tothe pixels A, B, and C as described above. The three movable mirrorelements corresponding to the pixels A, B, and C are irradiated with thelight from the light source 101 in a uniform manner and the relationshipbetween the received light intensity and the output is linear at thelight-receiving elements 110.

In the calibration mode TR, of the pixels A, B, and C, only the movablemirror element corresponding to the pixel B points in the OFF-direction.The light intensity measured by the light-receiving element 110corresponds to one third of the light intensity when all the movablemirror elements of the spatial light modulator 104 point in theOFF-direction. The operation unit 112, therefore, multiplies the outputof the light-intensity measuring section 110 by three to convert it to avalue when all the movable mirror elements point in the OFF-direction.Similarly, the operation unit 112 converts the output of thelight-intensity measuring section 110 to 1.5 times in the calibrationmode TB and to 1.0 time in the calibration mode TG. The light-sourcecontroller 114 controls the light intensity of the light source 101using the calculation by the operation unit 112.

In the projector 100 according to the exemplary embodiment, the lightsource 101 includes the plurality of LEDs. Thus, the irradiation of thespatial light modulator 104 is roughly shared by the LEDs of the lightsource 101. This may cause difference in light intensity measured by thelight-intensity measuring section 110 depending on the position of themovable mirror elements in the OFF-direction during the measurement ofthe light intensity. The error due to the position of the movable mirrorelements in the OFF-direction, out of the movable mirror elements of thespatial light modulator 104, may be corrected by the calculation by theoperation unit 112, which allows more accurate stabilization of thelight intensity.

The output of the light-intensity measuring section 110 is calculated bythe operation unit 112 in accordance with the image signal. Thus, thelight intensity of the light source 101 can be controlled to a specifiedvalue irrespective of the number or the position of the movable mirrorelements in the OFF-direction. Since the light intensity is controlledirrespective of the number or the position of the movable mirrorelements in the OFF-direction, as described above, the light intensityof the light source 101 can be stabilized and uniformized even duringimage projection while the movable mirror elements are being driven,thus providing the projector 100 that projects images having an alwaysbright, stable, and uniform luminance.

The operation unit 112 according to the exemplary embodiment performs aspecified operation using the number of movable mirror elements thatreflect the light from the light source 101 in the direction other thanthat of the projector lens 106. The invention, however, is not limitedto that. The calculation method by the operation unit 112 can be variedas appropriate depending on the intended use of the projector 100, thusproviding a projector that controls the light intensity depending on theuse condition or the requirements of the user.

According to the exemplary embodiment, the light source 101 includes aplurality of LEDs. The invention, however, may be applied to a structurein which the light source 101 is constructed of a single light-emittingelement. The conjugate arrangement of the light-emitting element and thelight-intensity measuring section 110 allows the stabilization of thelight intensity of the light source 101 without loss of the brightnessof the projection image, thus providing the projector 100 capable ofprojecting bright and stable images.

Second Exemplary Embodiment

FIG. 5 shows a schematic of a projector 500 according to a secondexemplary embodiment of the invention. The same components as those ofthe first exemplary embodiment are given the same reference numerals andtheir redundant description will be omitted. A light source 501 of theprojector 500 includes a first light source 501RB that emits light in afirst wavelength range and a second light source 501G that emits lightin a second wavelength range different from the first wavelength range.The light source 501 denotes both of the first light source 501RB andthe second light source 501G hereinafter. The first light source 501RBincludes an R-light LED 502R that emits R-light and a B-light LED 502Bthat emits B-light. The second light source 501G includes G-light LEDs502G that emit G-light. The first light source 501RB and the secondlight source 501G are arranged in approximately symmetrical positionswith respect to the optical axis AX of the projector lens 106.

FIG. 13 shows examples of the respective lighting time and half-toningtime of the color-light LEDs of the light source 501. The light source501 illuminates the spatial light modulator 104 in one frame of aprojection image by lighting on the R-light LED 502R, the G-light LED502G, and the B-light LED 502B in sequence. An observer integrates theR-light, the G-light, and the B-light, emitted from the light source 501in sequence and modulated by the spatial light modulator 104, torecognize them. A full-color projection image is thus formed on thescreen 108.

To obtain an entirely white projection image by the sequentialprojection of the R-light, G-light, and B-light, the amount of G-lightflux must be 60 to 80 percent of all the light flux. Assuming that theoutput amount and the number of the color-light LEDs are equal, theamount of G-light flux would become insufficient. Therefore, as shown inFIG. 13(a), the lighting time GT of the G-light LED 502G is made longerthan any of the lighting time RT of the R-light LED 502R and thelighting time BT of the B-light LED 502B. FIG. 13(b) shows the colortoning of the projection image by controlling half-toning time. Thehalf-toning time is the time period that the spatial light modulator 114needs to achieve intensity (tone) corresponding to the image signal foreach color light. The respective half-toning times agree with theperiods of the subframes of the images corresponding to the respectivecolor lights. When the tone of the image is represented by n-bit (n is apositive integer), the length of the unit bit of the G-light half-toningtime GK and the respective lengths of the unit bit of the R-light andB-light half-toning times RK and BK can be made different. When thenumber of the G-light LEDs 502G is larger than any of the numbers of theR-light LEDs 502R and the B-light LEDs 502B, the lighting time GT of theG-light LEDs 502G can be made equal to or shorter than the lighting timeRT of the R-light LED 502R and the lighting time BT of the B-light LED502B.

The R-light LED 502R and the B-light LED 502B and the G-light LED 502Gare arranged symmetrically with respect to the optical axis AX of theprojector lens 106, as described above. With such a structure, theversatility of arrangement is increased such that the G-light LEDs 502Gare arranged more than the R-light LED 502R and the B-light LED 502B.Thus, a projection image with color balance can be provided with asimple structure.

The movable mirror elements are driven in the +θ direction or the −θdirection in accordance with the image signals. In this way, the movablemirror elements of the spatial light modulator 104 shift selectivelybetween a first reflecting position and a second reflecting position, inaccordance with the image signals to reflect the incident light towardthe projector lens 106 (ON), or in the direction other than that of theprojector lens 106 (OFF). The light emitted from the first light source501RB and incident on the spatial light modulator 104, is reflectedtoward the projector lens 106 when the movable mirror element of thespatial light modulator 104 points in the +θ direction, whereas it isreflected in the direction other than that of the projector lens 106when the movable mirror element points in the −θ direction. In the framein which the R-light and the B-light are projected by the driving of thefirst light source 501RB, the movable mirror elements in the +θdirection reflect the light toward the projector lens 106. In the framein which the G-light is projected by the driving of the second lightsource 501G, the movable mirror elements in the −θ direction reflect thelight toward the projector lens 106. The driving polarity of the movablemirror elements is reversed among the lighting time GT of the G-lightLED 502G, the lighting time RT of the R-light LED 502R, and the lightingtime BT of the B-light LED 502B. The spatial light modulator 104 thusmodulates the light depending on the ON and OFF of the image signals,providing a full-color projection image.

In the projector 500 according to the exemplary embodiment, a secondlight-intensity measuring section 511 and the first light source 501RBare formed on an identical substrate 503. Light-receiving elements 510Gconstructing the second light-intensity measuring section 511 arearranged between the LEDs 502R and 502B, that are solid-statelight-emitting elements of the first light source 501RB, as will bedescribed later. The substrate 503 also includes the light-source drivecircuit 103 formed thereon. The light-receiving elements 510G arearranged in the image forming position of the second light source 501Gor in the vicinity thereof.

Similarly, a first light-intensity measuring section 510 and the secondlight source 501G are formed on the identical substrate 503.Light-receiving elements 510R and 510B, constructing the firstlight-intensity measuring section 510, are arranged between the LEDs502G that are solid-state light-emitting elements of the second lightsource 501G, as will be described later. The substrate 503 also includesthe light-source drive circuit 103 formed thereon. The light-receivingelements 510R and 510B are arranged in the image forming position of thefirst light source 501RB or in the vicinity thereof.

FIG. 6 shows a view as seen from the spatial light modulator 104 towardthe projector lens 106. Referring to FIG. 6, the arrangement of thecolor-light LEDs 502R, 502G, and 502B and the light-receiving elements510R, 510G, and 510B will be described. In the exemplary embodiment,when all the movable mirror elements are inclined at approximately 0°,the R-light LED 502R and the B-light LED 502B of the first light source501RB and the light-receiving elements 510R and 510B are conjugate witheach other, respectively. Similarly, when all the movable mirrorelements are inclined at approximately 0°, the G-light LEDs 502G of thesecond light source 501G and the light-receiving elements 510G areconjugate with each other.

The light emitted from the first light source 501RB will first bedescribed. The light from the first light source 501RB is modulated bythe spatial light modulator 104 and advances in the direction of theprojector lens 106 or in the direction other than that of the projectorlens 106. The light (OFF-light) advancing in the direction other thanthat of the projector lens 106 is reflected in the direction that formsan angle of +4θ with respect to the axis (for example, the optical axisof the projector lens 106) coupling the spatial light modulator 104 andthe projector lens 106. When the inclination of the movable mirrorelement is approximately 0°, the light emitted from the first lightsource 501RB is incident on the light-receiving elements 510R and 510Bwhich are arranged on the identical substrate 503 with the second lightsource 501G and which construct the first light-intensity measuringsection 510. The light-receiving elements 510R and 510B output signalscorresponding to the respective light quantities of the LEDs 502R and502B to an operation unit 512. The operation unit 512 makes acalculation based on the outputs from the light-receiving elements 510Rand 510B. The operation unit 512 outputs the calculation to alight-source controller 514. The light-source controller 514 controlsthe light-source drive circuit 103 in accordance with the output fromthe operation unit 512 to control the outputs of the first light source501RB for each of the LEDs 502R and 502B.

The light emitted from the second light source 501G will be describednext. The light from the second light source 501G is modulated by thespatial light modulator 104 and advances in the direction of theprojector lens 106 or in the direction other than that of the projectorlens 106. The light (OFF-light) advancing in the direction other thanthat of the projector lens 106 is reflected in the direction that formsan angle of −4θ with respect to the axis (for example, the optical axisof the projector lens 106) coupling the spatial light modulator 104 andthe projector lens 106. When the inclination of the movable mirrorelement is approximately 0°, the light emitted from the second lightsource 501G is incident on the light-receiving elements 510G which arearranged on the identical substrate 503 with the first light source501RB and which construct the second light-intensity measuring section511. The light-receiving elements 510G output signals corresponding tothe respective light intensities of the LEDs 502G to the operation unit512. The operation unit 512 makes a calculation based on the outputsfrom the light-receiving elements 510G.

The operation unit 512 outputs the calculation to the light-sourcecontroller 514. The light-source controller 514 controls thelight-source drive circuit 103 in accordance with the output from theoperation unit 512 to control the outputs of the second light source501G for each LED 502G.

In the exemplary embodiment, each of the movable mirror elements isgiven a reset signal at the timing when the subframes are switched.Given the reset signal, the inclination of the movable mirror elementthat is inclined at −θ or +θ becomes 0°. Specifically, the normal of themovable mirror element becomes substantially parallel with the opticalaxis of the projector lens by the reset signal. Thus, the firstlight-intensity measuring section 510 and the second light-intensitymeasuring section 511 make light-intensity measurements insynchronization with the timings of the reset signals.

The first light-intensity measuring section 510 to measure the lightfrom the first light source 501RB is arranged in the image formingposition of the first light source 501RB or in the vicinity thereof. Thesecond light-intensity measuring section 511 to measure the light fromthe second light source 501G is arranged in the image forming positionof the second light source 501G or in the vicinity thereof. Thus thefirst light-intensity measuring section 510 and the secondlight-intensity measuring section 511 can be arranged in correspondencewith the arrangement of the first light source 501RB and the secondlight source 501G. The first light source 501RB and the secondlight-intensity measuring section 511 are provided on the identicalsubstrate 503. The second light source 501G and the firstlight-intensity measuring section 510 are arranged on the identicalsubstrate 503. This allows space-saving and the reduction ofinstallation cost. As in the first exemplary embodiment, the opticalpath to form a projection image is not blocked off by thelight-receiving elements 510R, 510G, and 510B. Consequently, theprojector 500 can be provided with a simple structure in which theprojecting image is bright, stable, and uniform.

In the exemplary embodiment, for example, the light-receiving elements510G are arranged between the LEDs 502R and 502B on the identicalsubstrate 503. The tilt mirror devices generally modulate the light fromthe light source 501 by selectively moving the reflection surfaces ofthe movable mirror elements. The movable ranges of the movable mirrorelements are limited. Therefore, the deflection angle at which thespatial light modulator 104 reflects the incident light in the directionof the projector lens 106 or in the direction other than that of theprojector lens 106 (in the direction of the correspondinglight-receiving element) is also substantially limited. As in theexemplary embodiment, however, the mixed arrangement of, for example,the LEDs 502B and 502R and the light-receiving elements 510G maximizesthe utilization of the deflection angle of the spatial light modulator104. The maximum use of the deflection angle at the spatial lightmodulator 104 ensures the clearance between the light source 501 and thebarrel of the projector lens 106, reducing or preventing spatialinterference therebetween.

Third Exemplary Embodiment

FIG. 7 is a schematic of a projector 700 according to a third exemplaryembodiment of the invention. The same components as those of the firstexemplary embodiment are given the same reference numerals and theirredundant description will be omitted. The light source of the projector700 according to the exemplary embodiment includes a first light source701RB that emits light in a first wavelength range and a second lightsource 701G that emits light in a second wavelength range different fromthe first wavelength range as in the second exemplary embodiment. Thefirst light source 701RB includes an LED 702R that emits R-light and anLED 702B that emits B-light. The second light source 701G includes LEDs702G that emit G-light. The first light source 701RB and the secondlight source 701G are arranged in approximately symmetrical positionswith respect to the optical axis AX of the projector lens 106.

The first light source 701RB and a second light-intensity measuringsection 711 are formed on an identical substrate 703. The secondlight-intensity measuring section 711 is constructed of light-receivingelements 710G. The second light source 701G and a first light-intensitymeasuring section 710 are formed on the identical substrate 703. Thefirst light-intensity measuring section 710 is constructed oflight-receiving elements 710R and 710B. The substrate 703 also includesthe light-source drive circuit 103 thereon.

FIG. 8 shows a view as seen from the spatial light modulator 104 towardthe projector lens 106. Referring to FIG. 8, the arrangement of the LEDsand the light-receiving elements will be described. The firstlight-intensity measuring section 710 is arranged in a region differentfrom the second light source 701G. The LEDs 702G constructing the secondlight source 701G and the light-receiving elements 710R and 710Bconstructing the first light-intensity measuring section 710 are eacharranged in a concentrated manner. Similarly, the second light-intensitymeasuring section 711 is arranged in a position different from the firstlight source 701RB. The LEDs 702R and 702B constructing the first lightsource 701RB and the light-receiving elements 710G constructing thesecond light-intensity measuring section 711 are each arranged in aconcentrated manner. The R-light LEDs 702R and the B-light LEDs 702B andthe light-receiving elements 710R and 710B are substantially conjugatewith each other, as in the second exemplary embodiment. The G-light LEDs702G and the light-receiving elements 710G are also substantiallyconjugate with each other, as in the second exemplary embodiment.

In the exemplary embodiment, the first light-intensity measuring section710 is arranged in a region different from the second light source 701G.The second light-intensity measuring section 711 is arranged in a regiondifferent from the first light source 701RB. Thus, the light-receivingelements 710R, 710G, and 710B are thermally and electrically isolatedfrom the LEDs 702R, 702G, and 702B. The light-receiving elements 710R,710G, and 710B are less influenced by heat propagation and electricalnoise from the LEDs 702R, 702G, and 702B, thus making a measurement withless error, and providing the projector 700 having a stable brightnessintensity and more accurate uniformity.

The first exemplary embodiment, the second exemplary embodiment, and thethird exemplary embodiment include, for example, an equal number of LEDsand light-receiving elements 710R, 710G, and 710B, which have one-to-onecorrespondence to each other to measure the light intensity (forexample, refer to FIG. 8). However, the invention is not limited tothat. Taking the projector 700 of the third exemplary embodiment as anexample, it is also possible that the number of the light-receivingelements 710R, 710G, and 710B is made smaller than that of the LEDs, inwhich the light from the LEDs is concentrated to the light-receivingelements 710R, 710G, and 710B, and detected, or, alternatively, thenumber of the light-receiving elements 710R, 710G, and 710B is madelarger than that of the LEDs, in which the light from the LEDs isdispersed to the light-receiving elements 710R, 710G, and 710B, anddetected. When the number of the light-receiving elements 710R, 710G,and 710B is smaller or larger than that of the LEDs, the light intensityof the light source 701 can be stabilized and uniformized by changingthe calculation method by an operation unit 712 as appropriate.

In the second exemplary embodiment and the third exemplary embodiment,for example, the light-receiving elements 710R, 710G, and 710B arearranged on the substrate 703 of the light source 701. However, theinvention is not limited to that. Taking the projector 700 of the thirdexemplary embodiment as an example, the positions, where thelight-receiving elements 710R, 710G, and 710B to be arranged, can bechanged as appropriate, as far as they are in the vicinity of the lightsource 701 and in the position where the image of the light source 701can be substantially imaged. The light-receiving elements 710R, 710G,and 710B, however, need to be placed in positions where the light fromthe light source 701, which is near the light-receiving elements 710R,710G, and 710B, is not blocked off.

Fourth Exemplary Embodiment

FIG. 9 shows a schematic of a projector 900 according to a fourthexemplary embodiment of the invention. The same components as those ofthe first exemplary embodiment are given the same reference numerals andtheir redundant description will be omitted. As in the second exemplaryembodiment, the exemplary embodiment includes a first light source 901RBthat emits light in a first wavelength range and a second light source901G that emits light in a second wavelength range different from thefirst wavelength range. The first light source 901RB includes an LED902R that emits R-light and an LED 902B that emits B-light. The secondlight source 901G includes LEDs 902G that emit G-light. The first lightsource 901RB and the second light source 901G are arranged inapproximately symmetrical positions with respect to the optical axis AXof the projector lens 106. In the exemplary embodiment, the first lightsource 901RB also functions as the second light-intensity measuringsection of the second exemplary embodiment and the second light source901G also functions as the first light-intensity measuring section.

FIG. 10 shows a view as seen from the spatial light modulator 104 towardthe projector lens 106, and illustrating the arrangement of the lightsources 901RB and 901G. When the movable mirror elements are inclined atapproximately 0°, the R-light LEDs 902R and the B-light LEDs 902B of thefirst light source 901RB are arranged in the positions where the secondlight source 901G forms an image or in the vicinity thereof. When themovable mirror elements are inclined at approximately 0°, the G-lightLEDs 902G of the second light source 901G are arranged in the positionswhere the first light source 901RB forms an image or in the vicinitythereof. Accordingly, when the movable mirror elements are inclined atapproximately 0°, the R-light LEDs 902R and the B-light LEDs 902B, andthe G-light LEDs 902G are substantially conjugate with each other.

FIG. 11 shows a circuit schematic to switch the functions of thelight-emitting elements and the light-receiving elements of the LEDs902R, 902G, and 902B. Since every circuit configurations of the LEDs arethe same, the LED 902R will be described by way of example. In orderthat the LED 902R functions as light-emitting element, a terminal SW1 isselected, in which case R-light L is generated from the LED 902R by thedrive current from the light-source drive circuit 103.

In order that the LED 902R functions as light-receiving element, aterminal SW2 is selected. The LED 902R outputs a current correspondingto the detected light and sends it to an operation unit 912. Therefore,the LED 902R can be switched between a light-emitting mode and alight-receiving mode in a time division manner by the switching of ananalog switch 920. The LED 902R is driven in accordance with an imagesignal sent from an image transmitter (not shown), and switched to alight-receiving mode at a later-described measuring timing, therebymeasuring light intensity.

Since the LED 902R also functions as light-intensity measuring section,there is no need to have a separate light-receiving element. Since thelight-receiving element is not needed, the number of components can bereduced, allowing space-saving for the structure to measure lightintensity and reduction in installation cost. Thus the versatility ofthe LEDs 902R, 902G, and 902B of the light source is increased, so thatthey can be arranged in a small area. Therefore, the first and secondlight sources 901RB and 901G can be made closer to a point source, whichis ideal for the lighting of the projector 900. Consequently, theprojector 900 can be provided which is capable of projecting a bright,stable, and uniform projection image with a simple structure.

The operation and the timing to measure light intensity will next bedescribed. FIG. 12 shows an example of the timing of measuring lightintensity by the LEDs. The timing chart of FIG. 12 is for one frame of aprojection image, showing the respective operating time (lighting time)and the measuring time (light-receiving time) of the color LEDs 902R,902G, and 902B, the respective image signals of pixels, and themeasurement timings by the LEDs, from the top. The chart is representedin a positive logic system.

The spatial light modulator 104 reflects the light from the first lightsource 901RB toward the projector lens 106 when the movable mirrorelements point in the +θ direction, whereas when the movable mirrorelements point in the −θ direction, the spatial light modulator 104reflects the light from the first light source 901RB in the directionother than that of the projector lens 106. The method to control themovable mirror elements is the same as that of the third exemplaryembodiment.

As shown in the timing chart of FIG. 12, the timing is proactivelyprovided to make the inclination angles of all the movable mirrors to 0°by sending a reset signal to the frame (subframe) of each color light,at least one time, to set a calibration mode. The light from the R-lightLED 902R and the B-light LED 902B is measured by the G-light LED 902G ofthe second light source 901G in conjugate relation. The light-sourcedrive circuit 103 switches the analog switch 920 of the G-light LED 902Gto the terminal SW2 at the respective calibration timings TR and TB inthe R-light frame and the B-light frame, in accordance with the imagesignal.

Similarly, the light from the G-light LED 902G is measured by theR-light LED 902R or the B-light LED 902B in conjugate relation. Theanalog switch 920 of the R-light LED 902R or the B-light LED 902B isswitched to the terminal SW2 at the calibration timing TG in the G-lightframe.

The driving polarity of the spatial light modulator 104 is reversedbetween the period during which the R-light LED 902R and the B-light LED902B emit light and the period during which the G-light LED 902G emitslight, as in the second exemplary embodiment.

While the R-light LED 902R is emitting light, the G-light LED 902Glights off and functions as light-receiving element. At that time, theinclination angles of the movable mirror elements of the spatial lightmodulator 104 corresponding to pixels A, B, and C are made from −θ or +θto 0° (or horizontal) in the calibration period TR by the reset signal.Thereby the light from the R-light LED 902R is incident on the G-lightLED 902G functioning as light-receiving element. Thus the G-light LED902G measures the light intensity of the R-light.

Similarly, while the B-light LED 902B is emitting light, the G-light LED902G lights off and functions as light-receiving element. At that time,the inclination angles of the movable mirror elements of the spatiallight modulator 104 corresponding to the pixels A, B, and C are madefrom −θ or +θ to 0° (or horizontal) in the calibration period TB by thereset signal. Thereby the light from the B-light LED 902B is incident onthe G-light LED 902G functioning as light-receiving element. Thus theG-light LED 902G measures the light intensity of the B-light.

While the G-light LED 902G is emitting light, the B-light LED 902B andthe R-light LED 902R light off and function as light-receiving element.At that time, the inclination angles of the movable mirror elements ofthe spatial light modulator 104 corresponding to the pixels A, B, and Care made from −θ or +θ to 0° (or horizontal) in the calibration periodTG by the reset signal. Thereby the light from the G-light LED 902G isincident on the B-light LED 902B and the R-light LED 902R functioning aslight-receiving element. Thus the B-light LED 902B and the R-light LED902R measure the light intensity of the G-light.

In the example of FIG. 12, the calibration mode is set one time in eachcolor-light frame in the frame of the projection image; however, variousmodifications may be made, for example, in which, for one frame in theprojection image, the calibration mode is set only in an R-light frameand, for the next frame, the calibration mode is set only in a G-lightframe. When a plurality LEDs are provided for each color light, thelight intensity of an individual LED for each color light can bemeasured by providing the calibration mode during only a single LED foreach color light is lit on, thereby allowing the light intensity to becontrolled for each color light and each LED.

The calibration timing can be set freely as in the first exemplaryembodiment. Furthermore, the invention can apply to the structure inwhich the calibration timing is set by proactively providing the timingat which all the movable mirror elements are pointed in theOFF-direction (refer to FIG. 12), and the structure in which thecalibration timing is provided irrespective of the number of theOFF-light mirrors (refer to FIG. 4) and using the calculation by theoperation unit 912.

In the above description, the R-light LED 902R and the B-light LED 902B,and the G-light LEDs 902G are substantially conjugate with each otherwhen the inclination angles of all the movable mirror elements are 0°,so that the total sum of the R-light LEDs 902R and the B-light LEDs 902Bis equal to the number of the G-light LEDs 902G. The exemplaryembodiment, however, is not limited to that; the number of thecolor-light LEDs can be varied as appropriate depending on thestructure, the application and so on of the projector 900, so that thenumber of the R-light LEDs 902R and the B-light LEDs 902B and the numberof the G-light LEDs 902G may be different from each other. For example,when the number of the R-light LEDs 902R and the B-light LEDs 902B islarger than the that of the G-light LEDs 902G, R-light and B-light arecollected more to the G-light LED 902G and measured, and G-light isdispersed more to the R-light LED 902R or the B-light LED 902B andmeasured. In this case, appropriate calculation by the operation unit912 allows the light intensity of the light sources 901RB and 901G to bestabilized and uniformized, as in the case where the number of theR-light LEDs 902R and the B-light LEDs 902B is equal to that of theG-light LEDs 902G.

When the light source includes a plurality of LEDs for each color light,it is also possible that only some of the LEDs are switched between thelight emission and the light reception and other LEDs emit light only.In this case, light is collected to the LED having a light-receivingfunction and its light intensity is measured. Appropriate calculation bythe operation unit 912 allows the light intensity of the first lightsource 901RB and the second light source 901G to be stabilized anduniformized, as in the exemplary embodiment capable of switching betweenthe light emission and the light reception for all the LEDs.

When the temperature is high owing to the light emission by the LEDs, anerror may arise during the light intensity measurement because thetemperature is still high when the mode is switched to a light-receivingmode. The error in the light intensity measurement makes it difficult tosufficiently stabilize and uniformize the light intensity of the lightsource 901. Therefore, a temperature sensor (not shown) may be providednear the LEDs to correct the output of the receiving LEDs on the basisof the temperature of the LEDs and to thereby correct the error due tothe change in temperature of the LEDs. The LEDs in the light-receivingmode may function as temperature sensor in the state in which no lightis received and no light intensity measurement is made. Therefore, aspecific LED of the LEDs in the light-receiving mode can be used only astemperature sensor. Accordingly, it is also possible to detect thetemperature with the LED used as temperature sensor and to therebycorrect the error due to temperature change.

The exemplary embodiment is constructed such that the R-light, G-light,and B-light LEDs make light emission and light reception. In this case,the received-light detection sensitivity sometimes varies depending onthe color combination of the emission-mode LEDs and the reception-modeLEDs. In this case, when the light intensity measurement is performedwhile the variation in detection sensitivity is corrected, the outputsof the LEDs of the light source 901 can be controlled uniformly. Thewavelength range of the light from the emitting LEDs (for example,R-light from the R-light LED 902R) is sometimes low in detectionsensitivity for the receiving LEDs (for example, the G-light LED 902G).Even in this case, the light intensity of the light from the lightsource 901 can be sufficiently measured because the wavelengthdistribution characteristic of LEDs is relatively wider than that oflaser or the like and illuminating LEDs have high outputs.

Fifth Exemplary Embodiment

FIG. 14 shows a schematic of a printer 1400 according to a fifthexemplary embodiment of the invention. The same components as those ofthe first exemplary embodiment are given the same reference numerals andtheir redundant description will be omitted. The printer 1400 includesan illuminator 1401, an imaging lens 1402, and a reflecting mirror 1403.The illuminator 1401 principally has the same components as those of theprojector 100 of the first exemplary embodiment, except the projectorlens 106. The light intensity of a light source of the illuminator 1401is controlled as in the above exemplary embodiments. The light emittedfrom the illuminator 1401 forms an image on a photographic paper Pthrough the imaging lens 1402. The reflecting mirror 1403 is arranged tobend the light from the imaging lens 1402 toward the photographic paperP.

The DMD, the spatial light modulator 104 in the illuminator 1401,includes, for example, movable mirror elements of 16 μm square perelement arranged with a 1 μm spacing two dimensionally on a substrate.The ON/OFF of the respective regions of the movable mirror elements iscontrolled by controlling the rotation of the movable mirror elements.As for the exemplary embodiment, the movable mirror elements in thespatial light modulator 104 are controlled so as to reflect the lightfrom the light source in the illuminator 1401 toward the imaging lens1402, so that the very small areas on the photographic paper P whichcorrespond to the movable mirror elements are exposed to light.

When the movable mirror elements in the spatial light modulator 104 arecontrolled so as to reflect the light from the light source in thedirection other than that of the imaging lens 1402, the very small areason the photographic paper P which correspond to the movable mirrorelements are not exposed to light. Such control is made for each movablemirror element, so that a specified region 1404 on the photographicpaper P is exposed to form a dot image (a latent image).

The spatial light modulator 104 includes movable mirror elementsarranged two dimensionally, for example, as a mirror array of 192scanning lines, so as to be able to expose a plurality of scanninglines, perpendicular to the carrying direction of the photographic paperP, to light at the same time. The photographic paper P is continuouslycarried in the direction of the arrow A. The spatial light modulator 104reflects the R-light, G-light, and B-light, which are applied in timesequence, so as to form a color image on the photographic paper P byexposing light to the paper, thereby providing the full color image onthe photographic paper P. The details of the operation of the printer ofthe type that exposes photographic paper are described in, for example,JP-A-2001-133895.

The light source of the illuminator 1401 has the same structure as thatof the projector according to the above exemplary embodiments and iscontrolled as in the above exemplary embodiments, thereby allowing thestabilization of the light intensity of the light source withoutdecreasing efficiency, and thus providing the efficient and stableprinter 1400. The optical device according to an aspect of the inventionhas been described taking a printer as an example, which performsexposure on photographic paper; however, the invention is not limited tothe printer. The invention can easily be applied to any optical devicesthat require illumination light that is bright and uniform inilluminance distribution. For example, the invention may be effectivelyalso applied to a semiconductor exposure device or the like. In theabove exemplary embodiments, the solid-state light-emitting element hasbeen described with the LED as an example. However, a semiconductorlaser device and an electroluminescent (EL) device or the like may beused.

1. A projector, comprising: a light source to emit light; a spatiallight modulator to modulate the light from the light source inaccordance with an image signal; a light-intensity measuring section tomeasure light intensity; a light-intensity controller to control lightintensity in accordance with a signal from the light-intensity measuringsection; and a projector lens to project the light modulated by thespatial light modulator, the spatial light modulator including aplurality of movable mirror elements reflecting the light from the lightsource in a direction of the projector lens or in the direction otherthan that of the projector lens, and the light-intensity measuringsection measures the light intensity of the light reflected in thedirection other than that of the projector lens.
 2. A projectoraccording to claim 1, wherein the light source includes a solid-statelight-emitting element.
 3. A projector according to claim 2, wherein thesolid-state light-emitting element is one of an LED, a semiconductorlaser device, and an electroluminescent device.
 4. A projector accordingto claim 1, wherein the light source includes a plurality of solid-statelight-emitting elements; the light-intensity measuring section includesa plurality of light-intensity measuring elements corresponding to theplurality of solid-state light-emitting elements; and thelight-intensity controller controls each of the plurality of solid-statelight-emitting elements.
 5. A projector according to claim 1, furthercomprising an operation unit for performing a specified calculationbased on the signal from the light-intensity measuring section andoutputting the calculation to the light-intensity controller.
 6. Aprojector according to claim 5, wherein the operation unit performs thespecified calculation using the number of the movable mirror elementsreflecting the light from the light source in the direction other thanthat of the projector lens.
 7. A projector according to claim 1, whereinthe light source comprises a first light source for emitting light in afirst wavelength range and a second light source for emitting light in asecond wavelength range different from the first wavelength range; thefirst light source and the second light source are arranged inapproximately symmetrical positions with respect to the projector lens;and the light-intensity measuring section comprises a firstlight-intensity measuring section and a second light-intensity measuringsection, wherein the first light-intensity measuring section is arrangedin the vicinity of the second light source and out of the light from thefirst light source, measures the light intensity of the light reflectedin the direction other than that of the projector lens; and the secondlight-intensity measuring section is arranged in the vicinity of thefirst light source and out of the light from the second light source,measures the light intensity of the light reflected in the directionother than that of the projector lens.
 8. A projector according to claim7, wherein the first light-intensity measuring section and the secondlight source are formed on an identical substrate, the firstlight-intensity measuring section being arranged among the plurality ofsolid-state light-emitting elements of the second light source; and thesecond light-intensity measuring section and the first light source areformed on an identical substrate, the second light-intensity measuringsection being arranged among the plurality of solid-state light-emittingelements of the first light source.
 9. A projector according to claim 7,wherein the first light-intensity measuring section and the second lightsource are formed on an identical substrate, the first light-intensitymeasuring section being arranged in a region different from the secondlight source; and the second light-intensity measuring section and thefirst light source are formed on an identical substrate, the secondlight-intensity measuring section being arranged in a region differentfrom the first light source.
 10. An optical device, comprising: a lightsource to emit light; a spatial light modulator to modulate the lightfrom the light source in accordance with an image signal; alight-intensity measuring section to measure light intensity; alight-intensity controller to control light intensity in accordance witha signal from the light-intensity measuring section; and an imaging lensto image the light modulated by the spatial light modulator onto aspecified surface, the spatial light modulator including a plurality ofmovable mirror elements reflecting the light from the light source in adirection of the imaging lens or in the direction other than that of theimaging lens, and the light-intensity measuring section measures thelight intensity of the light reflected in the direction other than thatof the imaging lens.
 11. An optical device according to claim 10,wherein the light source includes a solid-state light-emitting element.12. An optical device according to claim 11, wherein the solid-statelight-emitting element is one of an LED, a semiconductor laser device,and an electroluminescent device.